The present invention generally relates to a device for controlling transmission of vibrations from machinery to their environment and vice-versa. More particularly, the present invention relates to a passive micro vibration isolator for the suppression of a broad band of vibration frequencies. The invention further relates to ZK washers for use in such isolators as an alternative to known Belleville washers.
In general, vibration originating from machines or other sources is most often undesirable and detrimental. For example, vibration in a precision machining tool may lead to faults and imperfections in work pieces produced on the tool. The vibration also may be transmitted through the floor and disrupt other tools. Additionally, the noise generally associated with machine vibration may be disruptive to workers.
Various methods and devices exist to reduce undesirable vibrations and may be generally categorized as vibration isolators or suppressors. Typically, vibration isolation devices operate locally to reduce transmissibility, wherein transmissibility is typically defined as the ratio of the transmitted force to the disturbing force. As such, vibration isolation devices are particularly suitable for reducing discrete and transient vibrations. For example, where a CMP machine may rest on a platform, various reflexive and absorptive materials such as rubber may be placed between the platform legs and the floor to isolate the machine from any vibrations coming from the floor.
Vibration mitigation devices may be categorized further as active or passive devices. Typically, active devices incorporate a feedback system which detects the amplitude and/or frequency of the disrupting vibration and responds accordingly to reduce or eliminate the vibration. Therefore, active devices are capable of broadband reduction of vibration. However, the complexity and cost of typical active devices often make them impractical for many applications.
In contrast, passive devices are typically mechanical devices which generally use various spring elements and damping elements to reduce or eliminate vibrations. However, conventional passive devices generally operate to reduce vibrations only in a fairly narrow bandwidth. Additionally, certain materials used in conventional passive devices, such as rubber and lubricating fluid, may be inappropriate for use in certain environments, such as clean room environments.
In conventional devices, a spring element is commonly used in combination with a beam-column element to reduce the transmission of vibration. See U.S. Pat. No. 5,178,357, issued on January 1993, to Platus and related U.S. Pat. No. 5,549,270, issued on August 1996, to Platus et al. More particularly, a spring and a beam-column are calibrated such that one element has a positive stiffness and the other element has an equal negative stiffness. In this manner, an object is supported with near-zero effective stiffness. However, a spring and beam-column pair is required for each axis to be isolated from vibration and each spring and beam-column pair must be precisely calibrated to achieve a net-zero effective stiffness in each axis. As such, this method is fairly complicated and difficult to calibrate and adjust. Additionally, as the requisite negative and positive stiffness are achieved through two separate elements, if one element wears at a rate different than that of the other, their stiffness will no longer match and a net-zero effective stiffness will not be achieved. Moreover, conventional devices typically require a good deal of maintenance and are too sensitive or fragile to support large, heavy and especially sensitive equipment such as CMP machines and powerful microscopes.
The present invention relates to a passive vibration isolation device for reducing vibration transmissibility in a broad frequency range. In a preferred exemplary embodiment of the present invention, a vibration isolation device includes a plurality of net-zero or near-zero effective stiffness elements. More particularly, a configuration of balls trapped between raceways is used in combination with springs, conic washers and the like with substantially zero tangent stiffness at large secant stiffness, such as, for example, non-linear springs, Belleville, ZK washers or any combination of the same. In addition, another configuration facilitates the reconfiguration of the non-linear springs to tune them for lighter and heavier loads.